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The VR-4 has been stuttering while cold for the last five or six months. Only when it's sat overnight and started in the morning. Felt like it was missing; checked intake tract, no leaks, ECU has had its capacitors replaced, plugs and wires are fine. Couldn't figure it out.

Today I started it after it sat a couple days (from the busted wheel) and took it out, and it did its usual stuttering business. I was watching the logger and saw nothing odd, so I floored it and the car began to accelerate and then the power fell way off and the stuttering went through the roof; then I looked out the rear view and saw the huge cloud of black smoke :D Something is definitely make the car run EXTREMELY rich when cold. Once it heats up it runs fine. Anyone see this behavior before and fix it?
 

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Absolute amateur guess - maybe one of your sensors is stuck on giving a reading that is normal for a hot engine. Since you have a pocketlogger, look at the numbers, and see if they differ from normal when the engine is cold.

For example, when the engine is cold, does the coolant temperature say it's 195 degrees? - that kind of stuff.
 

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More Than Meets the Eye
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Are the plugs gapped small? The usual .028-.030 gap required to prevent blowout also means they don't fully ignite fuel. The only way around this part that I know of is a coil kit so you can open the gap up again.

I'll be doing that shortly.
 

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Start by checking the plugs.

If all of them are black/sooty, you have a fuel problem (too rich)

You may also find the "one" plug that is causing your problem. A mis-firing plug causes a classic "studder" followed by a puff of black smoke when it starts hitting.

Again, start by inspoecting the front three plugs to see if you are burning rich in all cylinders or just missing on one.



Clint
 

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OMT

O2
Don't think about blaming O2 sensors for your woes. They cannot cause the car to run THAT rich. (They only provide a ~5% change in F/A mixture. Might srew up your mileage and emmission tests but no clouds of smoke from O2. The O2 sensors are also INACTIVE until they get up to temperature so they CANNOT be blamed for any behavior when the car first starts. )

ECU
Could be caused by failing ECU but I would not expect the symptom to go away so easily when the car warms up. My bet is still on a bad plug (s).


Clint
 

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Ninja Performance
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When COLD your O2 senser is not warmed up enuf and reads lean which may cause the computer to dump more fuel to get it to go more rich when in fact it is rich but the O2 is not warm enuf to see that.
 

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Imp Pwr Online

I actually posted my comments about O2 before you posted your comments. IMHO O2 sensors have been blamed for too many problems that cannot be attributed to a bad O2 sensor.


Clint
 
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